Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Fresh snowfall has improved the riding but increased the areas where you can get into trouble. Triggering a large avalanche on a buried weak layer remains a concern. Slabs of snow reactive to a rider's weight can be found in areas open to the wind and in wind-sheltered locations. Loose surface snow may sluff, run long distances, and entrain enough snow to become dangerous. Cold temperatures require a short and simple plan for a successful day.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    Weak snow 1-3 feet below the surface remains a lingering hazard. It remains possible for a rider to trigger a slide that fails at the weak layer producing a large avalanche. Natural or human-triggered avalanches in Sunday's storm snow have the potential to step down and initiate a slide deeper in the pack. Managing this problem is tricky and best done through terrain selection. Stick to slopes less than 35 degrees and not connected to steeper terrain above. 

    (12/14/2022) No propagation in this ECTN(11) test. Again that odd double fracture was visible.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Sunday, observers noted the storm snow was developing into soft slabs in areas sheltered from the wind later in the day. Drifting snow is forming slabs on slopes open to the wind. Slides have the potential to entrain substantial amounts of loose surface snow. Cracking at the surface indicates a slab and signifies that you should find another slope to enjoy. Mitigate this problem by choosing terrain less than 35 degrees in steepness and free of terrain traps.

    (12/18/2022)

    An overproducing storm formed thin soft slabs in the new snow by day's end. 

    Photo: Erich Peitzsch

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Observations Sunday noted up to 1 foot of new, very low-density snow and 2 feet of cohesionless surface snow in sheltered locations. On steep slopes, natural sluffing occurred, and skiers easily triggered sluffs ascending and descending. Once initiated, sluffs can potentially entrain substantial amounts of surface snow. Steer around long-running gullies and limit time spent above terrain traps where debris can pile up deep. Choosing slopes with a lower slope angle not connected to steep terrain above will limit exposure to this problem.

    (12/18/2022)

    Sluffing in the new snow was common as an overproducing storm left up to 1 foot of low-density snow. Natural and triggered sluffs occurred on steep terrain and entrained substantial snow.

Avalanche Discussion

Sunday's observations came from experienced users who chose sheltered terrain to mitigate the north-through-east winds associated with the arctic air. All reports mentioned extremely low-density new snow up to 1 foot deep that easily sluffed. Loose Dry slides occurred naturally and were often initiated with snow falling from trees. Riders triggered sluffs both on the ascent and descent. Slides entrained surface snow and grew large enough to become dangerous. As the new snow piled up, soft slabs developed. We expect these slabs to have continued developing with continued snow overnight. 

We have added Storm Slab and Loose Dry to today's avalanche problem list. This is the first time these problems have been on our product this season. Generally, both of these problems heal quickly and are removed a couple of days after the storm ends. However, cold temperatures slow the strengthening process and may affect their removal.

We have incorporated wind slabs into today's storm slab problem as we expect slabs to be found in both sheltered terrain and areas open to the wind. Slabs formed from drifting snow may be found in all aspects. Most weather stations report winds from the north through east direction; however, southwest flow continues at Sperry and Aeneas. Winds on Aeneas Ridge have been cranking for the past 48 hours averaging 25 mph with gusts up to 61!

Cold air continues to infiltrate the Flathead, with temperatures cooler this morning at all stations than Sunday. The epicenter of the arctic air remains the Essex to Marias Pass corridor, where the Snowslip station (6950 feet) high temperature over the past 24 hours is negative19 F. The cold air has finally enveloped the Whitefish Range, with Stahl Peak reporting 24 degrees cooler this morning. The WMR summit station is an excellent example of how a wind shift can immediately affect the ambient air temperature. The winds shifted from the south to the north-northwest Sunday night, dropping the temperature 14 F in one hour. A few hours later, the winds moved southwest, raising temperatures 12 F in one hour.

Bitterly cold temperatures appear to stick around throughout the workweek. If you are heading out to enjoy the soft snow, developing a simple and short plan for your adventure is imperative. Remember, equipment and humans don't function well in these conditions, and a minor problem can develop into a severe emergency. 

Training: Now's a great time to hone your companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. You can get more details about training and education opportunities events on our events calendar.

Observations - Thanks to everyone who's been utilizing our new observation submission page. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as specific or vague as you want. Our new Observation View page highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives.

 

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